My suggestion would be to talk to your doctor. While a Water Fast isn't inherently bad, it's supposed to reset your body and release all the toxins from out of your body. Your steroid injections may through your body out of wack, but if it is an anti-inflammatory you should be fine. Still, this is all supposition and hypothesizing. So definitely still talk this over with your GPA. If he/she doesn't condone your water fast, tell him/her that you will continue to do it anyway-- you just wish to hear their advise, so that you can make your fast a healthier one.